This invention relates, in general, to sealing devices and, in particular, to a system and method for creating a fluid seal between production tubing and well casing by energizing a seal element positioned around a section of the production tubing.
Without limiting the scope of the present invention, its background will be described with reference to producing fluid from a subterranean formation, as an example.
After drilling each of the sections of a subterranean wellbore, individual lengths of relatively large diameter metal tubulars are typically secured together to form a casing string that is positioned within each section of the wellbore. This casing string is used to increase the integrity of the wellbore by preventing the wall of the hole from caving in. In addition, the casing string prevents movement of fluids from one formation to another formation.
Conventionally, each section of the casing string is cemented within the wellbore before the next section of the wellbore is drilled. Accordingly, each subsequent section of the wellbore must have a diameter that is less than the previous section. For example, a first section of the wellbore may receive a conductor casing string having a 20-inch diameter. The next several sections of the wellbore may receive intermediate casing strings having 16-inch, 13xe2x85x9c-inch and 9⅝-inch diameters, respectively. The final sections of the wellbore may receive production casing strings having 7-inch and 4xc2xd-inch diameters, respectively. Each of the casing strings may be hung from a casinghead near the surface. Alternatively, some of the casing strings may be in the form of liner strings that extend from near the setting depth of previous section of casing. In this case, the liner string will be suspended from the previous section of casing on a liner hanger.
Once this well construction process is finished, the completion process may begin. For example, the completion process may include creating hydraulic openings or perforations through the production casing string, the cement and a short distance into the desired formation or formations so that production fluids may enter the interior of the wellbore. In addition, the completion process may involve formation stimulation to enhance production, gravel packing to prevent sand production and the like. The completion process also includes installing a production tubing string within the well that extends from the surface to the production interval or intervals.
Unlike the casing strings that form a part of the wellbore itself, the production tubing string is used to produce the well by providing the conduit for formation fluids to travel from the formation depth to the surface. In addition, tools within the tubing string provide for the control of the fluids being produced from the formation. For example, the production tubing string typically includes one or more seal assemblies. The seal assemblies may be installed above and below a production interval to isolate the production from that interval or a single seal assembly may be installed at a depth slightly above the casing perforations in a well having a single completion or at the deepest completion. In this case, the end of the production tubing string may be left open to allow production fluid to enter the production tubing. Once the seal assembly is properly positioned, the seal assembly is actuated to create a sealing and gripping relationship with the walls of the adjacent casing or liner. Accordingly, in the single seal assembly case discussed above, the seal assembly seals the annular space between the production tubing and the casing above the perforations such that the produced fluids that flow through the perforations must enter the open end of the tubing string.
To achieve the gripping relationship, typical seal assemblies are equipped with anchor slips that have opposed camming surfaces that cooperate with complementary opposed wedging surfaces. The anchor slips are radially extendable into gripping engagement against the well casing bore in response to relative axial movement of the wedging surfaces. To achieve the sealing relationship, typical seal assemblies carry annular seal elements that are expandable radially into sealing engagement against the bore of the well casing in response to an axial compression force. Mechanical or hydraulic means typically may be used to set the anchor slips and the sealing elements. For example, the mechanically set seal assemblies may be actuated by pipe string rotation or reciprocation. Alternatively, mechanically set seal assemblies may be actuated by employing a setting tool that is run downhole and coupled to the seal assembly for setting. Likewise, hydraulically set seal assemblies may be actuated using a setting tool that is run downhole and coupled in fluid communication with the seal assembly. Alternatively, elevating the fluid pressure within the tubing string may be used to actuate hydraulically set seal assemblies.
It has been found, however, that each of these conventional setting operations is suitable only when the seal assembly is positioned within a string of jointed tubing wherein relative rotation between the pipe string and the seal assembly is possible or wherein mechanical or hydraulic access if available to the seal assembly from the interior of the pipe string. Accordingly, such conventional seal assemblies using conventional setting techniques are not suitable for use with continuous tubing such as coiled tubing or composite coiled tubing.
Therefore a need has arisen for a seal assembly that is capable of creating a sealing and gripping relationship between a continuous tubing and a well casing. A need has also arisen for a method for assembling such a seal assembly for use on continuous tubing. In addition, a need has arisen for a method of actuating such a seal assembly to create the sealing and gripping relationship between a continuous tubing and a well casing.
The present invention disclosed herein comprises a downhole seal assembly that is capable of creating a sealing and gripping relationship between a continuous tubing and a well casing. The seal assembly of the present invention may be assembled to the exterior of the continuous tubing. In addition, the seal assembly of the present invention may be actuated downhole to create the sealing and gripping relationship between a continuous tubing and a well casing.
In one aspect, the present invention is directed to a seal assembly for controlling the flow of fluids in a wellbore. The seal assembly may be positioned on a section of continuous tubular such as a section of composite coiled tubing which may include a plurality of composite layers, a substantially impermeable material lining an inner surface of the innermost composite layer forming a fluid passageway and an operating fluid conduit integrally positioned between two of the composite layers. The seal assembly includes a mandrel having a flange that is positioned around the section of the tubular. First and second slip ramps are positioned around the mandrel. Anchor slips are positioned around the mandrel between the first and second slip ramps such that the anchor slips may be radially extended into a gripping engagement against the wellbore in response to relative axial movement of the first and second slip ramps toward one another.
The seal assembly also includes a setting assembly that is positioned around the mandrel and in fluid communication with the operating fluid conduit. The setting assembly is hydraulically actuated to axially shift the first slip ramp toward the second slip ramp. The seal assembly also has a seal element positioned around the mandrel between the flange and the second slip ramp. The seal element is actuatable into a sealing engagement with the wellbore in response to a compressive axial force applied to the seal element between the second slip ramp and the flange after actuation of the setting assembly.
In one embodiment, the seal element may comprise a sheet that is wrapped around the mandrel to form a plurality of layers. In another embodiment, the seal element may comprise a plurality of arc shaped segments that are positioned around the mandrel to form an annular member. In yet another embodiment, the seal element may comprise first and second sections having a jointed slidably engagable relationship. The first and second sections may each have a plurality of seal members that form a sealing engagement with the wellbore in response to the first and second sections being axially shifted toward one another. In another embodiment, the seal element may comprise a spoolable member that is wound around the mandrel to form a plurality of turns.
In the wrapped, segmented and spoolable embodiments of the seal element, the seal element may comprise elastomers, rubbers, or other material suitable for sealing. The seal element may be subjected to a crosslinking reaction to increase the strength and resiliency of the extrudable material and to unitize the seal element. The crosslinking reaction may be vulcanization, a radiation crosslinking reaction, a photochemical crosslinking reaction, a chemical crosslinking reaction or other suitable reaction.
In another aspect, the present invention is directed to a method for assembling a seal assembly on a tubular having an operating fluid conduit associated therewith. The method comprises positioning a mandrel having a flange around the exterior of the tubular, disposing first and second slip ramps around the mandrel, positioning anchor slips around the mandrel between the first and second slip ramps, coupling a setting assembly around the mandrel, establishing fluid communication between the operating fluid conduit and the setting assembly and positioning a seal element around the mandrel between the flange and the second slip ramp.
In another aspect, the present invention is directed to a method for operating a seal assembly. The method comprises disposing the tubular within a wellbore, communicating an operating fluid to the setting assembly through the operating fluid conduit, axially shifting the first slip ramp toward the second slip ramp with the setting assembly, radially expanding the anchor slips into gripping engagement with the wellbore in response to the relative axially movement of the first and second slip ramps and radially expanding the seal element into sealing engagement with the wellbore in response to a compressive axial force applied to the seal element between the second slip ramp and the flange.